Load-settlement behavior of elastic-perfectly plastic GRFB A. Dey Former Research Scholar, Department of Civil Engineering, Indian Institute of Technology, Kanpur-208016,UP, India P. K. Basudhar Professor, Department of Civil Engineering, Indian Institute of Technology, Kanpur-208016,UP, India ABSTRACT: This paper presents an innovative technique to estimate the collapse load of a strip footing rest- ing on reinforced elastic-perfectly plastic bed subjected to monotonically increasing load and predict the cor- responding load-settlement behavior. The foundation is represented by linear/nonlinear Winkler springs, and the footing and the geosynthetic reinforcement are modeled with the aid of the flexural beams. In order to de- termine the load-settlement behavior of the foundation, an iterative process has been developed and reported. In the analysis, the newly developed technique uses the concepts of local yield load and ultimate load. The successful application of the proposed method has been demonstrated with an example problem. For typical cases, the ultimate load determined for a nonlinear Winkler foundation is found to be 20-100 times higher than that for a linear Winkler medium. 1 INTRODUCTON Prediction of the response of footings resting on reinforced elastic foundations using lumped para- meter approach is a very interesting and fairly re- searched topic in geotechnical engineering [Mad- hav and Poorooshasb (1988), Ghosh and Madhav (1994), Shukla and Chandra (1994), Yin (1997, 2000), Maheshwari et al. (2004), Deb et al. (2005c), Dey and Basudhar (2008)]. The load- settlement behavior of such foundation systems till failure and the determination of the ultimate load is, however, not so widely explored. Based on a number of experimental observations, Huang and Menq (1997) proposed a regression relationship to determine the ultimate bearing capacity of a strip footing resting on reinforced foundation. Using limit state method, Michalowski (2004) provided an expression to determine the ultimate bearing capacity for a footing resting on a single layer of reinforcement. However, till now, based on lumped parameter modeling, no attempt has been made to determine the load-settlement behavior of reinforced elastic foundations subjected to mono- tonically increasing load and considering progres- sive failure. Hence, an effort has been made in this aspect to study the load-settlement behavior of a footing resting on a reinforced elastic-perfectly plastic foundation and determine the local yield and ulti- mate loads of the same; the same has been reported in this article. Lumped parameter approach has been used for the study using both linear and non- linear Winkler springs. To interpret the results considering linear Winkler springs and determine the local yield and ultimate load of the foundation, a new technique has been devised based on the generated contact stresses exceeding the ultimate bearing capacity of the reinforced foundation bed and the subsequent development of plastic zone beneath the footing. For the case considering non- linear springs, the conventional double-tangent method [Vesic (1973)] has been used to determine the ultimate load of the geosynthetic reinforced foundation bed (GRFB). It has been observed that the ultimate load obtained considering the nonli- near Winkler springs are 20-100 times than that obtained considering linear Winkler springs. 2 ULTIMATE BEARING CAPACITY OF REINFORCED FOUNDATION BED Based on a number of experimental observations, Schlosser et al. (1983) proposed the failure pattern occurring for a footing resting on a reinforced gra- nular bed as depicted in Fig. 1. Fig. 1 Failure mechanism of reinforced ground and load- distribution angle [Schlosser et al. (1983)]. Considering the above failure mechanism, and based on a number of experimental observations, Huang and Menq (1997) proposed the relationship